Apparatus and method for anhysteretically recording from master drum to slave web

Abstract: A ported vacuum drum (20, 56-98) is provided on its exterior cylindrical surface (22) with one or more lengths (24) of a master magnetic recording medium supported by bands (102) of elastomeric material in position to contact a layer (14) of slave magnetic recording medium provided on one side and along at least one edge of a web (10); so that, vacuum applied (74-82) between the cylindrical surface and the web at locations (88-94) spaced from the zone of contact (98) between the recording media will hold the slave layer on the web securely in contact with the length of master magnetic recording medium on the drum as the drum rotates, thereby permitting anhysteretic recording from the master to the slave. A method of anhysteretically recording is taught.

Description: Field of the Invention The invention concerns transferring recorded information from one magnetic medium to another. More particularly, the invention concerns apparatus and methods for anhysteretically recording from a high coercivity master medium carried on a rotatable, circular cylindrical drum to a lower coercivity slave medium carried on a web of indeterminate length wrapped on the drum; so that, information previously recorded on the master medium is recorded repeatedly along the length of the slave medium as the cylindrical drum rotates and the web translates in contact with a portion of the cylindrical drum. Background of the Invention Conventional magnetic recording requires a stationary recording head which makes contact with a moving surface of a magnetic medium, which may be in web, disk or drum form. Because of the tendency of such heads to abrade the magnetic medium, at least the surface layer of the magnetic medium generally is made from a durable material selected to resist abrasion. In recent years, photographic films have been developed which include on one side of a base material, various layers of photosensitive materials; and on the other side, a thin, virtually transparent layer of magnetic medium. The magnetic medium can be used, for example, during manufacture of the film to record information related to the film's characteristics; during use of the film in the camera to enable the camera to read and adjust itself in response to previously recorded information, or to record information about camera settings and scene characteristics, or both; and during processing or developing of the film to enable the processing equipment to read previously recorded information and adjust the processing parameters accordingly. However, because of the presence of the magnetic medium in a photographic film, the properties of the surface layer of the magnetic medium are chosen more for their photographic suitabilities than for their resistance to the sort of abrasion which can occur due to contact with a stationary recording head in a conventional recording process. Any abrasion on the film surface must be avoided since it would degrade the optical properties of the film and thereby prevent capture and reproduction of high quality images. As a result, if conventional recording apparatus were used to record to the magnetic recording medium on such a film, there would be a danger that the magnetic medium would be damaged due to abrasion. Use of a contact head is acceptable in a camera due to the low speed of recording and reading but would not be acceptable in a high speed film manufacturing process. Moreover, even if a small amount of abrasion were acceptable, the abraded material would tend to build up on the recording head, thereby increasing the gap between the head and the recording medium and potentially degrading the signal applied to the recording medium to an unacceptable level. Also, such abraded material would tend to break loose from the head, resulting in loose dirt on the film which would degrade performance. Another type of recording process, known as anhysteretic recording, has been used for many years for duplication of magnetic media, particularly video and audio tapes, without requiring the use of a recording head which may abrade the duplicate or slave medium. In this process, a master magnetic medium is prepared which typically has a magnetic coercivity about two to three times higher than the coercivity of the slave medium on which duplicate copies are to be made. The master medium may be provided in web or drum format and is prerecorded, using a conventional contact recording head, with the information to be duplicated. The master medium and the slave medium are then brought into intimate, stable contact, with no relative motion, in the presence of a decaying, alternating magnetic bias field; so that, a mirror image of the information on the master is transferred to the slave. Problems to be Solved by the Invention Since there is no abrasion between the master and slave media in conventional apparatus and processes useful for anhysteretic recording, the application of such apparatus and processes to record to photographic film having a magnetic medium would appear promising. However, recording to a photographic film introduces a number of problems not found in conventional duplicating of video and audio tapes. For example, applications for still camera photography will require recording of digital signals of relatively low bit density due to the characteristics of the magnetic medium on the film, likely no higher than 1000 bits per inch (39.4 bits per millimeter) which means that recording onto the film must be done with a very high degree of reliability since redundant recording will not be feasible. Much higher bit densities typically are used for data, video and audio applications, such as 10,000 bits per inch (394 bits per millimeter) for digital tape, 6,000 bits per inch (236 bits per millimeter) for floppy disks and 10,000 bits per inch (394 bits per millimeter) for Winchester disks. So that conventional, contact head equipment for reading the signals recorded to the photographic film will not damage the central image area of the film, it is desired to record only along the very edges of the film, rather than in the central portion of the magnetic medium as would be the case for non-photographic applications. Because the well known anticlastic effect will cause the edges of the slave medium to curl away slightly from an underlying master medium in drum format, intimate contact may be reduced in the very area where recording is desired. This effect is more pronounced with a photographic film than with a conventional magnetic tape for given levels of tension and elastic modulus, since the film is several times thicker than such tape. Moreover, air tends to become entrained during recording between the slave and master media which causes loss of intimate contact and prevents good signal transfer from the master medium to the slave medium, particularly at higher web velocities and with wider webs. Pinch rollers have been used to squeeze air from between the media; but with a pressure sensitive photographic film, such rollers are undesirable since they may cause images on the exposed film to exhibit unsightly pressure marks. Various types of air clamping devices are also known which apply elevated pressure air to the media to force air from the interface and bring the media into the desired intimate contact. However, such devices tend to be very noisy, can actually cause instabilities by forcing air into the interface and are expensive to operate due to their continuous need for compressed air. Where the master medium and the slave medium are both in web format, recording onto a slave photographic film with the magnetic medium on the back of the film in some arrangements would require that the emulsion side of the film be in contact with a backing roll for the master and slave media, which may cause damage to the emulsion. Thus, a need has existed for improvements to conventional apparatus and methods for anhysteretic recording to suit them for recording to photographic films bearing magnetic media. More particularly, a need has existed for anhysteretic recording apparatus and methods which can record along the edges of a photographic film with low signal density and low loss of signal and which can efficiently remove air from the interface between the media being recorded at high speeds, without risking pressure marking of or other damage to the film. A need has existed for such an apparatus which is readily manufactured with conventional technology; is compact; and can use renewable, conventional recording tape for the magnetic master, which may be prerecorded. Summary of the Invention The apparatus of the invention is useful for anhysteretically recording information onto a first web bearing a first, magnetic recording medium, the first web having a first pair of opposed edges separated by a first width of the first web. In a preferred embodiment, the apparatus comprises a circular cylindrical drum having a first exterior cylindrical surface with a second pair of opposed edges separated by a second width at least as long as the first width. At least one annular band of elastomeric material is supported by and extended around the drum, the band of elastomeric material having a second exterior cylindrical surface concentric with the first exterior cylindrical surface. At least one length is provided of a second web having a third exterior surface, the second web comprising a second, magnetic recording medium, the second web further having an interior surface adhered to the second exterior cylindrical surface, the elastomeric material at the second exterior cylindrical surface and the second web at the interior surface being mutually adherent directly to one another. The second web is supported by and extended as a band of the second, magnetic recording medium around the second exterior cylindrical surface. The band of the second, magnetic recording medium is in position to contact the first, magnetic recording medium, when the first web is wrapped onto the drum, to anhysteretically transfer information in an annular zone defined by an interface between the second web and the first web. Means associated with the drum are provided for applying subatmospheric pressure at the first exterior cylindrical surface at locations spaced from the annular zone, to cause the first web to establish intimate contact with the second web in the annular zone. The interface between the second web and the first web may occur along either or both of the pair of edges of the first web. The elastomeric material may have a Shore A hardness in the range of 10 to 40 durometer. The elastomeric material may be a polyester polyurethane; the interior surface of the second web may comprise a surface layer of polyester contacting the polyurethane; and the second web may have a thickness in the range of 0.00025 to 0.0035 inch (0.00064 to 0.0089 cm). The length of the second web comprises first and second ends, the ends being butted to one another on the second exterior cylindrical surface. In one embodiment of the invention, there are two of the bands of the second, magnetic recording medium to contact the first, magnetic recording medium in a pair of the annular zones, one along each of the first, opposed edges of the first web. The opposed edges of the first web may be positioned essentially midway of the corresponding edges of the bands of the second, magnetic recording medium. Except for the presence of the annular band of elastomeric material and the second, magnetic recording medium, the cylindrical drum may be of the general type shown in commonly assigned U.S. Patent 3,630,424, incorporated into this specification by reference, which is provided in the familiar manner with a stationary interior porting unit to limit the application of vacuum to a portion of the circumference of the drum. The first, magnetic recording medium may be of the type shown in commonly assigned U.S. Patents Nos. 3,782,947 and 4,320,523 and in commonly assigned published International Application No. WO 91/11750. The second, magnetic recording medium may be of the type discussed in European Patent Application No. 0550351. The means for applying subatmospheric pressure may comprise a plurality of circumferential grooves in the first exterior cylindrical surface; a plurality of axial grooves in the first exterior cylindrical surface, the axial grooves intersecting the circumferential grooves; a plurality of radial bores extending from the grooves into the drum; and means for applying subatmospheric pressure to the radial bores over an arc of a circumference of the drum, whereby subatmospheric pressure is applied between the first web and the drum. The first, magnetic recording medium may have a coercivity in the range of one-third to one-half the coercivity of the second, magnetic recording medium. The apparatus of the invention may further comprise means for driving the drum at a preferably constant velocity to meter the first web through the apparatus; though some variation in velocity is tolerable. A first means, upstream of the drum, applies tension to the first web approaching the drum; and a second means, downstream of the drum, applies tension to the first web leaving the drum. Alternatively, the apparatus may further comprise means for mounting said drum for rotation in response to movement of the first web; means for applying tension to the first web approaching the drum; a metering roll downstream of the drum; means for driving the metering roll at an essentially constant velocity to meter the first web through said apparatus; and means for applying tension to the first web leaving the metering roll. In both cases, an essentially constant velocity is preferred to facilitate stabilization of the interface between the two webs. The method of the invention is useful for anhysteretically recording information on a first web bearing a first, magnetic recording medium, the web having a first pair of opposed edges separated by a first width of the web. A circular cylindrical drum is provided having a first exterior cylindrical surface with a second pair of opposed edges separated by a second width at least as long as the first width. At least one annular band of elastomeric material is supported by and extended around the drum, the band of elastomeric material having a second exterior cylindrical surface concentric with the first exterior cylindrical surface. At least one length of a second web is provided, the length having a third exterior surface, the second web comprising a second, magnetic recording medium and an interior surface adhered to the second exterior cylindrical surface. The length of the second web extends as a band of the second, magnetic recording medium around the second exterior cylindrical surface. The band of the second, magnetic recording medium thus is in position to contact the first, magnetic recording medium, when the first web is wrapped onto the drum, to anhysteretically transfer information in an annular zone defined by an interface between the second web and the first web. The first web is wrapped around an arc of the first exterior cylindrical surface to define the interface between the first, magnetic recording medium and the second, magnetic recording medium. Subatmospheric pressure is applied through the first exterior cylindrical surface at locations spaced from the annular transfer zone, to cause the first web to establish intimate contact with the second web in the annular zone. The drum is rotated; and a magnetic bias field is applied to cause the transfer. Advantageous Effects of the Invention A number of advantageous effects are achieved with the apparatus and method of the invention. The information to be recorded onto the second, magnetic recording medium can be recorded using standard techniques onto the second web before or after the length of web is wound onto the master drum, using a recording head which touches the surface of the second, magnetic recording medium. The second medium can be removed and replaced if worn or damaged or if different information is to be recorded. An intimate interface can be achieved between the first and second, magnetic recording media at the edges of the first web for web speeds as high as 600 feet (182.88 m) per minute for webs as thick as 0.0056 inch (0.014 cm). The apparatus and the magnetic media can be readily manufactured using currently available manufacturing techniques and can be easily maintained. Recording along the edges of the first web is achieved, though recording in the central area of the first web also can be achieved by reconfiguring the vacuum ports and relocating the elastomeric medium and the second, magnetic recording medium. The apparatus and method permit recording onto a mechanically sensitive web such as photographic film without damage to the film's mechanical or photographic properties. Brief Description of the Drawings The foregoing and other objectives, features and advantages of the invention will be apparent from the following more particular description of the preferred embodiments of the invention, as illustrated in the accompanying drawings. Figure 1 shows a schematic elevation view of one type of apparatus for anhysteretic recording embodying the invention. Figure 2 shows a schematic elevation view of another type of apparatus for anhysteretic recording embodying the invention. Figure 3 shows an elevation section view taken along line 3-3 of Figure 1, but with the first, magnetic recording medium omitted. Figure 4 shows an enlarged fragmentary section view of one edge of the recording drum, illustrating the locations of the elastomeric medium, the second, magnetic recording medium and the first, magnetic recording medium. For ease of illustration, a radial clearance is shown between the first medium and the recording drum; however, in operation no such clearance would exist. Figure 5 shows an elevation view as seen from the left of Figure 3. Figure 6 shows a fragmentary projected view of the array of axial and circumferential grooves and radial bores provided in the cylindrical surface of the drum of Figures 3 to 5 and illustrates the positions of the grooves and bores relative to the first and second, magnetic recording media. Figure 7 shows a fragmentary section view taken along line 7-7 of Figure 6. Description of the Preferred Embodiments The following is a detailed description of the preferred embodiments of the invention, reference being made to the drawings in which the same reference numerals identify the same elements of structure in each of the several Figures. As shown in Figures 1 and 2, the apparatus of the invention is particularly useful for recording onto a web 10 which comprises an acetate or plastic base having one side 12 with layers of photographic emulsions and another side 14 with a slave layer of a magnetic recording medium having a coercivity in the range of 500 to 1500 Oe. Web 10 is led into the apparatus of Figure 1 over an air bar or roller 16 with emulsion side 12 facing outward and then downward into a conventional infeed vacuum box 18 which maintains tension on the web, preferably in the range of 0.5 to 1.25 pounds per inch (0.089 to 0.223 kg per cm) of web width. After leaving vacuum box 18, web 10 is wrapped approximately 180° around a circular, cylindrical vacuum and recording drum 20 according to the invention, which in the embodiment of Figure 1 is driven at a constant speed by a motor, not illustrated. As seen schematically in Figure 1, drum 20 comprises an exterior cylindrical surface 22 which supports at least one length 24 of web comprising a master magnetic recording medium, of a type having a coercivity two to three times that of the medium on web 10, as described in published European Patent Application No. 0550351. In a preferred embodiment of recording drum 20 as best seen in Figures 3, 4 and 6, a pair of lengths 24 extend as continuous circumferential bands, one along each circumferential edge of drum 20; however, a single band along one edge of the drum or a band more toward the center of the circumferential surface of the drum is also within the scope of the invention. A preferred method for applying lengths 24 will be discussed later in this specification. As will be discussed in detail with regard to Figures 3 to 7, surface 22 is precisely machined to include an array 26 of axially and circumferentially extending grooves and radially extending ports which are in communication with a plurality of interior channels 28 within drum 20, only one of such channels 28 being illustrated for simplicity. As shown in phantom lines in Figure 1, such channels 28 communicate with a stationary interior porting unit having an approximately 180° exhaust port 30 connected to a suitable source of subatmospheric pressure. Thus, when surface 14 moves into contact with drum 20 opposite exhaust port 30, subatmospheric pressure is applied to the interface between surface 14 and surface 22 to remove entrained air via array 26 and thus to draw web 10 into intimate contact with surface 22 and lengths 24. Circumferential slip between web 10 and drum 20 also is eliminated. As drum 20 is rotated, it pulls web 10 along until channels 28 move out of communication with exhaust port 30, whereupon web 10 is released progressively from drum 20 to move into an outfeed vacuum box 32, from which it passes over a further air bar or roller 34 and out of the apparatus of the invention. Infeed vacuum box 18 provides a web tensioning and slack takeup link between the constant velocity drum 20 and the source of supply of web 10, not illustrated. Those skilled in the art will appreciate that a servo system, not illustrated, can be used to monitor the position of the loop of web 10 in vacuum box 18 and then to control the source of supply of web 10 as necessary to maintain an essentially constant position of the loop. The same sort of control scheme can be applied at outfeed vacuum box 32, except that loop position is maintained by controlling the rate of takeup of web 10 downstream of air bar 34. Thus web 10 is removed from infeed vacuum box 18 and added to outfeed vacuum box 34 by the continuous, preferably constant velocity rotation of drum 20, which acts as a web metering device. Web tension could also be maintained with a simple dancer or accumulator mechanism, as will be understood by those skilled in the art. While web 10 is being held in intimate contact with drum 20, a magnetic bias field is applied by either an array 36 of permanent bias magnets, of the type shown in commonly assigned U.S. Patent No. 5,179,475 issued 12 January 1993, or a conventional inductive bias head 38 or erase head of the type familiar to those skilled in the magnetic recording arts. For simplicity, both array 36 and magnet 38 are shown in Figure 1, though only one or the other would be used in an actual production apparatus. Array 36 and magnet 38 may be mounted on suitable movable stages to permit adjustment of the magnetic gap, as illustrated schematically. Due to the presence of the bias field and the intimate contact between web 10 and drum 20, information previously recorded on lengths 24 is anhysteretically recorded onto the magnetic recording medium on side 14 of web 10. For apparatus using array 36, the speed of drum 20 during anhysteretic transfer may be varied and can be quite high. However, when head 38 is used, operating speed also may be varied but may be limited by the maximum frequency at which the head can be driven reliably. Figure 2 shows another anhysteretic recording apparatus embodying the invention. Here, web 10 passes from vacuum box 18 over an air bar 40, over a roller 42, beneath an air bar or roller 44 and then wraps approximately 180° around drum 20, which in this instance is mounted for rotation as an idler roll. That is, drum 20 is not driven by a separate motor but rotates in response to movement of web 10. From drum 20, web 10 passes beneath an air bar or roller 46, an air bar or roller 48, and then wraps approximately 120° around a conventional, ported vacuum drum 50 which is driven at a constant speed by a motor, not illustrated, to pull web 10 through the apparatus. From metering drum 50, web 10 passes into outfeed vacuum box 32 before leaving the apparatus. A control scheme similar to that previously described can be applied to this embodiment of the apparatus of the invention. The apparatus of Figure 1 is advantageous since it does not require the web to provide the torque needed to overcome the inertia of drum 20, as in the case of the apparatus of Figure 2. Also, the apparatus of Figure 2 tends to cause more variation in web tension than that of Figure 1. In the embodiments of Figures 1 and 2, flanged rollers and edge guided air bars are used to provide good tracking and alignment to the vacuum drums. Turning to Figures 3 and 5, the apparatus of Figures 1 and 2 is mounted on a rigid, typically vertical face plate 52, illustrated in phantom lines. A port 54 extends through face plate 52 to provide passage for the drive shaft 56 which rotates drum 20 in the embodiment of Figure 1. In the embodiment of Figure 2, no drive shaft is provided but the structure of drum 20 is otherwise the same. On the front side of face plate 52, a cylindrical housing 58 is mounted by means of a spacer plate 60 and a plurality of bolts 62. Within housing 58, a cylindrical bearing housing 64 is mounted by a plurality of bolts 66. A central bore 68 in bearing housing 64 supports a pair of bearings 70, 72 for shaft 56. Surrounding the front end of bearing housing 64 is a vacuum stator ring 74 which comprises an approximately 180° exhaust plenum 30, as discussed with regard to Figure 1. A plurality of bolts 76 secure stator ring 74 to bearing housing 64. A passage 78 extends from exhaust plenum 30 through a flange 80 on bearing housing 64 and communicates with a connection port 82 for attachment to a source of subatmospheric pressure such as a vacuum pump, not illustrated. At the front end of shaft 56, a preferably stainless steel hub 84 is mounted by suitable fasteners. Hub 84 is press fitted into a bore within an annular titanium or aluminum vacuum drum rotor 86. Surface 22 preferably is right cylindrical but also could be contoured concavely to provide an increase in the normal force typically generated by tension in web 10. Such a contour would modify the tension profile in the web so that improved intimate contact would be established at the edges of the web where information transfer is to occur. As shown in Figures 3 to 7, around the circumference of rotor 86 are provided a plurality of axial bores 88, corresponding in function to channels 28 shown schematically in Figure 1, bores 88 being radially positioned to communicate with exhaust plenum 30 as drum 20 rotates, the opposite ends of bores 88 being plugged. The axial gap between stator ring 74 and rotor 86 is minimized to reduce vacuum leakage. A layer of a high lubricity material such as Teflon or Rulon, not illustrated, may be applied to the surface of stator ring 74 facing rotor 86, to reduce friction and provide a smooth wear-in surface should contact occur. Each axial bore 88 communicates with a plurality of radial bores 90 which preferably are approximately 0.031 inch (0.079 cm) in diameter and extend outward through surface 22. On the cylindrical surface of drum 20, array 26 preferably comprises a plurality of circumferential grooves 92 which preferably are 0.013 to 0.017 inch (0.033 to 0.043 cm) wide, 0.005 to 0.010 inch (0.0127 to 0.0254 cm) deep and spaced on a 0.052 inch (0.132 cm) pitch. Grooves 92 are intersected at bores 90 in an orthogonal array by a further plurality of axial grooves 94 which preferably are 0.010 inch (0.0254 cm) wide, 0.010 to 0.015 inch (0.0254 to 0.038 cm) deep and spaced on a 0.350 inch (0.889 cm) pitch. Other patterns of radial bores, axial grooves and circumferential grooves may be used without departing from the scope of the invention. In Figure 6, a length of the circumferential grooves has been omitted to show more clearly the relative positions of bores 88 beneath axial grooves 94. As shown schematically in Figure 6, a web 10 of width w preferably is somewhat narrower than the width W of drum 20. The presence of bores 90 and grooves 92, 94 could interfere with recording onto lengths 24 of master magnetic recording medium and with transfer of information from lengths 24 to slave magnetic layer 14. So, array 26 preferably is confined to the central portion of the exterior cylindrical surface 22 of drum 20, thus leaving on each edge of the cylindrical surface an annular zone 98 which preferably is wide enough to provide sufficient space for mounting of lengths 24 of master recording medium. When web 10 is wrapped onto drum 20, application of vacuum through bores 90 and grooves 92, 94 causes partial evacuation of air from between magnetic layer 14 and the surface of drum 20, thereby causing lengths 24 mounted in each of annular zones 98 to form an intimate interface with side 14 of web 10 to permit anhysteretic transfer of information from the master to the slave. That is, the radial clearance shown for ease of illustration in Figure 4 is eliminated upon application of vacuum to array 26. The edges of web 10 may be positioned essentially mid-way of the widths of lengths 24; however, the edge of web 10 may also extend beyond lengths 24. A vacuum in the range of 15 to 25 inches (38.1 to 63.5 cm) of mercury may be applied to ensure removal of entrained air and the necessary intimate contact. The vacuum applied is best at the center of array 26 but extends beyond the circumferential and axial grooves partially across annular zones 98 to ensure good contact with edge bands 99 on web 10. The quality of the vacuum achieved beneath web 10 can vary as a function of applied tension, anticlastic effect, curl induced in web 10 by relative humidity, edge burrs and the like. Preferably, a vacuum in the range of about 25 inches (38.1 to 63.5 cm) of mercury is applied at connection port 82 to ensure removal of entrained air and the necessary intimate contact. Lengths 24 of master magnetic recording medium preferably comprise an intrinsically high coercivity magnetic medium applied to a polyester support. As shown in Figures 3, 4 and 6, an annular circumferential groove 100 is provided along each edge of drum 20 and an annular band 102 of an elastomeric material is provided within each groove 100. The compliant drum surface helps to attenuate the effects of anticlastic edge curl and edge burrs, by allowing the drum to partially conform to the edge geometry of the medium, thereby providing an improved contact pattern. On a drum 20 having a diameter of about 4.0 inches (10.16 cm) and an axial width of about 2.0 inch (5.08 cm), groove 100 was about 0.09375 inch (0.238 cm) deep and about 0.5 inch (1.27 cm) wide. The width of groove 100 may be varied to accommodate various widths of lengths 24. Preferably, grooves 100 are positioned so that the edges of web 10 will be essentially midway of each band 102 and length 24 of the second, magnetic recording medium. Although it is preferred that grooves 100 be closed at their axial ends, it is also within the scope of the invention to provide grooves open to the ends of rotor 86. A process for applying such an elastomeric material is disclosed in European Patent Application No. 0542651 published 19 May 1993. Preferably, the elastomeric material has a Shore A hardness in the range of approximately 10 to 40 durometer, most preferably 20 to 25 durometer. In the one embodiment, a 0.09375 inch (0.238 cm) thick layer of low durometer polyester polyurethane was cast into circumferential groove 100. Band 102 is preferably applied to rotor 86 through a conventional casting process; however, it is also within the scope of the invention to cast band 102 separately and then adhere or otherwise attach it within groove 100. After band 102 has been applied within groove 100, conventional grinding techniques may be used to produce the desired surface finish and to obtain symmetry around the circumference of drum 20, so that surface 22 and the outer cylindrical surface of band 102 are concentric and of approximately the same radius. In one embodiment, the surface of the band 102 was ground to 16 RMS. Lengths 24 having the same widths as annular bands 102 are mutually adhered to bands 102 by wrapping them around drum 20 and trimming their ends to form smooth butt joints 104, as shown in Figure 6. As will be discussed in further detail, care must be taken when wrapping lengths 24 onto drum 20 to exert an essentially constant tension, in order to avoid differential stretching of the lengths which may influence their magnetic recording characteristics. Since lengths 24 are very thin, about 0.00025 to 0.0035 inch (0.00064 to 0.0089 cm), their extending above surface 22 does not interfere with establishing a good contact with surface 14 of web 10. To form the butt joints, a piece of metallic shim stock may be used as an anvil to cut lengths 24. Thin stainless steel strip approximately 0.001 inch (0.00254 cm) thick is preferred since it provides some flexibility to conform to the curvature of drum 20. The shim stock is used to support a length of the master magnetic recording medium as it is cut; therefore, length 24 initially needs to be large enough to cover the area over which a desired butt joint will be made. A first end of the length 24 is placed on annular band 102 and the rest of the length is wrapped circumferentially around drum 20. A slight, essentially constant tension is applied to provide a smooth, secure fit. For example, 0.5 lbs. (1.1 kg) tension is suitable for lengths 24 which are 0.5 inch (1.27 cm) wide and comprise a polyester base approximately 0.003 inch (0.008 cm) thick. An appropriately sized piece shim stock then is placed on annular band 102 under the first end of length 24 in the area where the second end of the length will overlap and the butt joint will be formed. Since the shim stock is thin and flexible, it conforms to the shape of drum 20, allowing length 24 to be positioned snugly against the surface of annular band 102. While maintaining tension on the second, outer end, a sharp knife is used to cut through both ends of length 24 above the shim stock. As shown in Figure 6, a diagonal butt joint 104 may be made. The shim stock and the waste pieces of length 24 are then removed; so that, the ends of length 24 will adhere directly to the elastomeric material of annular band 102, thereby forming a precision butt joint with a minimal gap. The resulting compliant magnetic drum provides continuous smooth surfaces for lengths 24 with radial compliance due to the elastomeric material and circumferential stiffness due to the lengths 24. Yet no separate mechanical elements are required to secure lengths 24 to drum 20. Successful recording from the master medium to the slave medium has been achieved as close as 0.020 inch (0.051 cm) to the edge of the slave medium, beyond which the anticlastic effect appeared to interfere with recording. For a given slave medium, the degree of anticlastic curl can be reduced by increasing the diameter of the recording drum. Lengths 24 and annular bands 102 are mutually adherent because the inherent surface free energy of the two materials permits the formation a secure bond. Although a good bond has been observed between polyester polyurethane in annular bands 102 and a polyester base for lengths 24, the use of other material couples is appropriate, where the surface free energies of the two materials are chosen to form such a secure bond; and where the hardness of the elastomeric material for annular bands 102 falls within the range previously discussed. This type of construction allows renewal of the master magnetic recording medium by removing the present length 24 and replacing it with a fresh length of master magnetic recording medium. However, it should be noted that the adherence between the elastomeric material and lengths 24 tends to increase with time, eventually making removal more difficult. The butt joint for strip 10 can be in a diagonal or axial direction. Figure 6 illustrates diagonal butt joints 104. As shown, each length 24 is discontinuous at the location of the butt joint. Accordingly, the loss of magnetic data may occur in this region. Therefore it may be desirable to use drum 20 such that less critical or no data is recorded in this region. The geometry of the butt joint may assist in minimizing the loss of magnetic data in this splice region. For example, if the data on drum 20 is read circumferentially, diagonal joint 104 would produce only a partial loss of data at any discrete circumferential position; whereas a straight butt joint, not illustrated, would produce a total loss of data at one discrete circumferential position. The strength of the bond formed between the base of length 24 and the elastomeric material of annular band 102 is influenced by the surface finish of band 102. The strongest bond has been observed on an unground, as cast elastomeric layer having a surface finish preferably less than 8 RMS. By grinding the outer diameter of band 102, reduced radial runout may be obtained; but the adhesion strength between length 24 and annular band 102 is decreased as the surface of band 102 is roughened. In one embodiment, the surface of band 102 was ground to 16 RMS, yet the decreased level of adhesion was found to be quite adequate. The thickness of length 24 also affects the bond to band 102, especially at the butt joint. Thinner materials, approximately 0.00025 to 0.0035 inch (0.00064-0.0089 cm) thick have less core set memory associated with circumferential beam stiffness and are therefore less likely to lose contact at the butt joint, compared to thicker materials of approximately 0.0045 inch (0.0114 cm) thickness. Therefore, lengths 24 made from such thicker materials may tend to unwrap themselves from band 102 at the butt joint, especially when length 24 is applied in the opposite rotational direction of its original core set.

Claims: Apparatus for anhysteretically recording information onto a first web (10) bearing a first, magnetic recording medium (14), the first web having a first pair of opposed edges separated by a first width (w) of the first web, the apparatus being of the type including a circular cylindrical drum (20) having a first exterior cylindrical surface (22) with a second pair of opposed edges separated by a second width (W) at least as long as the first width, characterized by: at least one annular band (102) of elastomeric material supported by and extended around the drum, the band of elastomeric material having a second exterior cylindrical surface concentric with the first exterior cylindrical surface; at least one length (24) of a second web having a third exterior surface, the second web comprising a second, magnetic recording medium, the second web further having an interior surface adhered to the second exterior cylindrical surface, the elastomeric material at the second exterior cylindrical surface and the second web at the interior surface being mutually adherent directly to one another, the length supported by and extended in a band of the second, magnetic recording medium around the second exterior cylindrical surface, the band of the second, magnetic recording medium being in position to contact the first, magnetic recording medium, when the first web is wrapped onto the drum, to anhysteretically transfer information in an annular zone (99) defined by an interface between the second web and the first web; and means (74, 78, 82, 86-94) associated with the drum for applying subatmospheric pressure at the first cylindrical surface at locations spaced from the annular zone, to cause the first web to establish intimate contact with the second web in the annular zone. Apparatus according to Claim 1, further characterized in that the interface between the second web and the first web occurs along at least one of the first pair of edges. Apparatus according to Claim 1, further characterized in that the elastomeric material has a Shore A hardness in the range of 10 to 40 durometer. Apparatus according to Claim 1, further characterized in that the elastomeric material is a polyester polyurethane; the interior surface of the second web comprises a surface layer of polyester contacting the polyurethane; and the second web has a thickness in the range of 0.00064 to 0.0089 cm. Apparatus according to Claim 4, the length of the second web comprises first and second ends, the ends being butted to one another on the second exterior cylindrical surface. Apparatus according to Claim 1, further characterized in that there are two of the bands of the second, magnetic recording medium to contact the first, magnetic recording medium in a pair of the annular zones, one along each of the first, opposed edges. Apparatus according to Claim 6, further characterized in that each of the first pair of opposed edges is positioned essentially midway of a corresponding one of the bands of the second, magnetic recording medium. Apparatus according to Claim 1, further characterized by: means (56-72) for driving the drum at an essentially constant velocity to meter the first web through the apparatus; a first means (18), upstream of the drum, for applying tension to the first web approaching the drum; and a second means (32), downstream of the drum, for applying tension to the first web leaving the drum. Apparatus according to Claim 1, further characterized by: means (52, 58-72) for mounting the drum for rotation in response to movement of the first web; means for applying tension to the first web approaching the drum; a metering roll (50) downstream of the drum; means for driving the metering roll at an essentially constant velocity to meter the first web through the apparatus; and means (32) for applying tension to the first web leaving the metering roll. A method for anhysteretically recording information on a first web (10) bearing a first, magnetic recording medium, the first web having a first pair of opposed edges separated by a first width (w) of the first web, the method characterized by the steps of: providing a circular cylindrical drum (20) having a first exterior cylindrical surface (22) with a second pair of opposed edges separated by a second width (W) at least as long as the first width; at least one annular band (102) of elastomeric material supported by and extended around the drum, the band of elastomeric material having a second exterior cylindrical surface concentric with the first exterior cylindrical surface; at least one length (24) of a second web having a third exterior surface, the second web comprising a second, magnetic recording medium, the second web further comprising an interior surface adhered to the second exterior cylindrical surface, the length extending in a band of the second, magnetic recording medium around the second exterior cylindrical surface, the band of the second, magnetic recording medium being in position to contact the first, magnetic recording medium, when the first web is wrapped onto the drum, to anhysteretically transfer information in an annular zone (99) defined by an interface between the second web and the first web; wrapping the first web around an arc of the first exterior cylindrical surface to define the interface between the first, magnetic recording medium and the second, magnetic recording medium; applying subatmospheric pressure through the first exterior cylindrical surface at locations spaced from the annular zone, to cause the first web to establish intimate contact with the second web in the annular zone; rotating the drum; and applying a magnetic bias field to cause the transfer.

Inventors: BIGELOW DONALD ORRIN, PALONE THOMAS WILLIAM, BIGELOW, DONALD ORRIN, PALONE, THOMAS WILLIAM, BIGELOW, DONALD ORRIN, C/O EASTMAN KODAK COMPANY, PALONE, THOMAS WILLIAM, C/O EASTMAN KODAK COMPANY
Applicants: EASTMAN KODAK CO, EASTMAN KODAK COMPANY
Application year: 1994
Main classification: G11B5
IPC codes: G03B17, G11B15, G11B5